Scala Bay Meetup - The state of Scala code style and quality
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Transcript of Scala Bay Meetup - The state of Scala code style and quality
Why care?
• Expressive language, haters like to call ‘complex’
• We’re reviewing code everyday
• Reduce number of moving parts
• Onboarding becomes easier
Questions
• What are the current code styles?
• Are we respecting them?
• What might become best practices/standard?
Gathered code styles• Official Scala Style
• Twitters Effective Scala
• Apache Spark
• Bizo Scala Style
• Kiji project
• Vertx mod lang
• Apache Kafka
Major differences
• Max 100 character line
• Do not use relative imports from other packages
• Always use braces for ifs except for ternary operator behavior
• Do not use infix notation if method is not an operator (map, filter, flatMap)
Major differences• Max 80 character line
• Declarations:
• Use vals when possible.
• Use private when possible for member variables.
• Use named arguments when passing in literal values
• Options should be used instead of null whenever possible
• Prefer case classes over tuples
Major differences
• Adds more than 40 rules to original style guide
• Introduces Collections, Object Oriented and Functional style advice
• Shows preferences over APIs
Conclusion
• Built upon Scala Style Guide
• 127 rules you can choose for your project
• Some differences are important enough to include in Official Scala Style
Answer by
• Analyzing open source projects for violations of Official Scala Style
• Understand % of compliance
• Understand number of code style violations
• Per category
• Per code pattern
Results
• 51% code style compliance on average
• Inverse correlation between Age of project and Code style compliance of project
• Correlation between number of committers and number of violations (expected)
BreakdownCurly braces
Line max
Method naming
catching Fatal exceptions
Mutable fields
object naming convention
class naming convention
others
Limitations of analysis
• Most popular tend to be libraries
• May not represent reality in industry perfectly
Conclusions
• 51% code style compliance on average
• Naming and formatting biggest culprits
• Older projects have less compliance
• Are we respecting them?
• Answer: we could do a better job.
Collapsing of containersOptions
if (startField.isEmpty && endField.isEmpty) Seq("foo", "bar")else if (startField.isEmpty && !endField.isEmpty) Seq("foo", endField.get)else if (!startField.isEmpty && endField.isEmpty) Seq(startField.get, "bar") else Seq(startField.get, endField.get)
Seq(startField.getOrElse("foo"),endField.getOrElse("bar"))
Vs
Collapsing of containers
Await.result(client.hGet(foo, bar)).get
client.hGet(foo, bar).map(f => ..)
Vs
Futures
Collections: optimizations• exists(x => x == b) replaceable with contains(b)
• .filter(x => ).head can be replaced with find(x => ) match { .. }
• .filter(x =>).headOption can be replaced with find(x => )
• .filter(x => Bool).isEmpty can be replaced with !exists(x => Bool)
• .filter(_.isDefined).map(_.get) can be replaced with flatten
• .filter(x => Bool).size can be replaced more concisely with with count(x => Bool)
• sort.filter can be replaced with filter.sort for performance
• !Traversable.isEmpty can be replaced with Traversable.nonEmpty
• !Traversable.nonEmpty can be replaced with Traversable.isEmpty
From Scapegoat
Akka
• Immutable messages
• If state becomes complex, context.become
• Not expose any state to outside
Guidelines
Unit testing
• Consistency in tests
• Encapsulate test state in a Context object.
Testing with state
Object oriented programming
• Use dependency injection for program modularization
• The use of traits are highly encouraged
• Do not use Exceptions for commonplace errors
• Encode commonplace errors explicitly: using Option or (scala.util./com.twitter.util.)Try
Functional programming• Options should be used instead of null whenever
possible
• Do not overuse Option: if there is a sensible default — a Null Object — use that instead.
• Don’t use pattern matching for conditional execution
• Only use call-by-name for creating new control constructs such as DSLs
• Prefer case classes over tuples (specially no ._1)
Note: Microservices
• Style of thinking and code in ‘Your Server as a Function’
• Server operations through future combinators
• Declarative programming
Microservices: declarative programming
recordHandletime andThentraceRequest andThencollectJvmStats andThenparseRequest andThenlogRequest andThenrecordClientStats andThensanitize andThenrespondToHealthCheck andThenapplyTrafficControl andThenvirtualHostServer